The present invention relates to an improved gauge for measuring the nip between a pair of rolls.
In manufacturing operations in which a sheet of material is squeezed through a rolling nip defined between a pair of rolls, such for example as in the production of hot rolled strip metal or paper, it is desirable that the nip be uniform in size along its length so that uniform pressures are exerted on the sheet of material. However, it often happens that variation in the radii of the rolls along their lengths, as well as nonparallelism of the rolls, lead to variations in nip size and therefore rolling pressures.
To determine the size of a rolling nip or variations thereof along its length, thereby to ascertain the pressures exerted on sheet material in the nip and/or roll adjustments necessary to eliminate or at least minimize any variations, the material may itself be examined after it has passed through the nip. However, it is usually more convenient to directly measure and obtain a profile of the size of the nip at various points along its length, and for the purpose nip gauges may be used.
One type of gauge for measuring the nip between a pair of rolls is disclosed in U.S. Pat. No. 4,186,579, which issued to Werner W. Eibe on Feb. 5, 1980. As taught therein, a device for measuring uniformity of pressure exerted in the nip between a pair of rolls comprises a body having a pair of support spheres which are held against the rolls and a sensing sphere at an end of a plunger carried in and urged outwardly of the body. The sensing sphere engages the circumference of the rolls, and a transducer generates signals representative of the amount of extension of the plunger from the body as a result of variations in the radii of the rolls.
Another nip gauge similar to that in said patent to Eibe is disclosed in German Pat. No. 826,201, which includes a body having a transducer therein and a plunger extending therefrom the end of which carries a pair of rollers. The rollers are moved toward the nip into engagement with the circumference of the rolls, and the transducer generates signals representative of the amount of extension of the plunger from the body as a result of the nip dimension.
Although the aforementioned nip gauges provide measurements of the size of the nip between a pair of rolls, the measurements are generally a linear function of roll radii or parallelism variations, and therefore are not extremely accurate with respect to any particular measurement. In addition, since it is necessary for the spherical tip or rollers to extend well into the nip to obtain accuracy, the tip or rollers must necessarily be quite small. When dragging along the nip, the spherical tip or rollers tend to jam and chatter, preventing smooth and accurate measurement taking. Thus, those gauges could not conveniently be used in obtaining, for example, a nip profile of supercalender rolls used in the papermaking industry, inasmuch as the surfaces of such rolls are formed of compressed cotton, and would therefore be prone to cause snagging if a gauge of the Eibe or German patent type were slid along the length of the nip. In addition, by virtue of the particular construction of the devices of Eibe and the German patent, the same are not suited for use in measuring the size of a nip between a pair of rolls of different diameters.